1. Field of the Invention
The invention relates to image processing apparatus and method for performing a color process.
2. Related Background Art
In recent years, it has become known that problems exist such that various color reconstructions are performed due to a difference of a coloring mechanism for each input/output device or a difference of a coloring material to be used. This is due to a spread of networks and an enlargement of a demand for a color product and that a color matching function differs for each kind of apparatus. There is a color management system (CMS), which is known as a technique which is highlighted to solve those problems. At present, to solve the problems, a process is executed for matching the colors of input and output images by connecting the system to a computer and performing a data conversion using profile data formed every input/output equipment by using a software (CMS software).
Even if the same signal is inputted, the same color is not always outputted due to a difference of the device. Therefore, information regarding characteristics of input/output signals in input/output equipment which was set in a reference state in order to suppress the characteristics of each device has been stored in the profile data. Input/output characteristics of the signal of the device are distinct by the profile data of each device and by correcting by using the profile data, the colors can be matched irrespective of the device.
The data conversion will now be described with reference to FIG. 13. In the diagram, device characteristics data regarding input equipment has been stored in input equipment profile data 101. Device characteristics data regarding output equipment has been stored in output equipment profile data 107.
A color signal obtained from the input equipment is converted by a data conversion unit 106 by using the input equipment profile data 101. The converted data is a color signal which doesn't depend in each device. In further another data conversion unit 112, the data is converted into a color signal suitable for each output equipment by using the output equipment profile data 107 and is outputted by using such a color signal.
At present, input/output equipment such as monitor, printer, scanner, or the like which is most frequently used has a function for changing the color or brightness in accordance with a taste of the user. The monitor generally has a knob to adjust the brightness and contrast. To obtain a preferable image in consideration of a fatigue of the eyes, the user can adjust the brightness of the monitor by freely moving the knob. In a monitor which can perform a further advanced correction, a formation of a gamma table, a change in color temperature of the monitor, and the like can be performed.
In a manner similar to the above, there is also a printer having the correcting function to obtain a desired color of the user by a method such that an output balance of colors is adjusted, an LUT is formed, or the like.
As mentioned above, when input/output equipment which can be adjusted by the user is used, there occurs a problem such that by the execution of the adjustment by the user, a state of the input/output equipment when the profile data is formed and a state of the equipment when data is actually inputted or outputted are different, so that an accurate color matching cannot be performed.
Such a problem also occurs in the color management system for performing a color matching process according to an illumination light, namely, a color managing technique which has been proposed in recent years.
A construction in the case where an image of an original is read by an image scanner and the read image is displayed on a monitor screen and an ambient light is considered will now be described. FIG. 14 shows a schematic constructional block diagram. An image scanner 510 reads out the image of the original and outputs the read image data in an (R, G, B) form. A scanner color conversion device 512 converts an output signal of an RGB colorimetric system of the scanner 510 into a standard colorimetric system (XYZ colorimetric system) with reference to a scanner profile 514 which has previously been formed from image reading characteristics of the image scanner 510.
A signal conversion device 516 corrects an output of the conversion device 512 in consideration of an ambient light in accordance with ambient color information which is supplied from the ambient light sensor 518 to detect color components or a color distribution of the ambient light.
In accordance with a monitor profile 522 which reflects coloring characteristics of a monitor display (hereinafter, abbreviated to a monitor) 524 to be used, a monitor color conversion device 520 converts the output signal of the XYZ colorimetric system of the signal conversion device 516 into values of an RGB space in consideration of the coloring characteristics of the monitor 524 and supplies the output signal to the monitor 524.
An environment where the image is observed will now be simply explained with reference to FIG. 15. A printed matter (original) 530 is read by the image scanner 510 and the read image is displayed as an image (original image) 532 on the screen of the monitor 524. The illumination light from a fluorescent light or the like illuminates an ambient portion as an ambient light 534. The ambient light sensor 518 is put onto the monitor 524, a printer, or a computer main body and detects a color distribution or color components of the ambient light 534. The original image 532 is generally displayed on the screen of the monitor 524 so as to be overlaid on a background color (color of the screen) 536. Therefore, the user simultaneously looks at both of the background color 536 and the original image 532 and recognizes the color of the original image 532.
The ambient light 534 changes depending on a situation. According to the existing color managing technique, the ambient light 534 is detected by the ambient light sensor 518 and, in accordance with the detection information, the signal conversion device 516 corrects an output of the scanner color conversion device 512, namely, the color signal of the standard colorimetric system. Thus, the coloring of the original image 532 which is displayed on the screen of the monitor 524 is adjusted in accordance with the ambient light. Namely, a colorimetrological coincidence is realized.
Although the colors of the same value on the standard color space inherently ought to be seen as a same color, in the case where both colors are a color of the monitor (light source color) and a color of the printed matter (object color) and even if they have the same value on the standard color space, they cannot be seen as a same color for the human eyes due to a difference of the visual environment, mode, or the like. As for such a problem, the following correcting techniques have also been proposed in order to enable the human being to perceive them as a same color by observing with the eyes.
It is considered that when observing colors, the human being uses white as a reference and recognizes all of the colors by comparing with white. It is now considered a case, as an example, of observing a monitor display image put under a certain ambient light and a printed matter put under the same or a different ambient light. There are a number of white colors which should be reference colors such as white of the monitor screen, white of the environmental light, white of a paper illuminated by the environmental light, and the like. It is possible to regard such that the colors are observed by using a white color adapted to such a number of white colors at a certain ratio as a reference. A method whereby by calculating reference white and converting the colors of all of the image by setting such white as a reference, observation colors are mutually matched is considered. Actually, when reference white is calculated, one adaptation ratio of white of the monitor screen under the fluorescent light to the ambient light is determined and reference white is calculated by using such an adaptation ratio.
As shown in FIG. 15, when observing the original image 532 which is displayed on the screen of the monitor 524, both of the original image 532 and the ambient color (background color) 536 simultaneously enter the eyes. Since the human being recognizes the color by a comparison with the circumstances, it is known that if the colors displayed in the center portion are the same and the background colors are different, the colors of different impressions are perceived. Therefore, even in case of displaying the same image, if the background color differs, the color of the display image is recognized as a different color.